In a manufacturing line for manufacturing mass products such as industrial products, a number of proportional solenoid valves are used for controlling flow rates and pressures of fluid. For example, in Japanese Patent Laid-Open Publication No. 2002-313753, a proportional solenoid valve is used for controlling an amount of cutting water supplied to a processing unit of a dicing apparatus. Fluid to be controlled by the proportional solenoid value includes a gas such as air, an inert gas, and vapor and a liquid such as water, heated water, a chemical solution, and oil. The proportional solenoid valve includes a valve body for adjusting a valve opening degree in a fluid flow path and a solenoid for generating an electromagnetic force in proportion to a driving signal supplied to a coil. A spring force in a direction of closing the fluid flow path is applied to the valve body by a spring member, so that the electromagnetic force generated at the solenoid against the spring force allows the valve body to open the fluid flow path and also allows the valve opening degree to change continuously in proportion to magnitude of the electromagnetic force.
A valve controller for controlling the driving signal is disposed near the proportional solenoid valve. The driving signal to be supplied from this valve controller to the coil of the proportional solenoid valve is controlled by this valve controller. When the proportional solenoid valve is used in a manufacturing line for manufacturing mass products, the driving signal is sent from the valve controller so that the valve body of the proportional solenoid valve can take any opening degree within a range of a valve fully-closing state to a valve fully-opening state, on the basis of a command signal which is inputted from a main controller such as a personal computer or other computers and corresponds to the valve opening degree. In a manufacturing line in which many proportional solenoid valves are used, for example, a command signal is inputted from one main controller in accordance with each valve controller of the proportional solenoid valves, so that the respective proportional solenoid valves are driven individually.
The command signal from the main controller to each valve controller depends on a characteristic of the main controller, and there are, for example, the case where a 4 to 20 mA current loop signal is outputted as a command signal and the case where a voltage signal within a range of 0 to 10 V is outputted as a command signal. For this reason, the valve controller is provided with an input signal selecting switch so that even when either command signal is inputted to the valve controller, the driving signal of the valve opening degree corresponding to the command signal can be outputted to the proportional solenoid valve. Therefore, for example, when a 4 mA current signal as the command signal for setting the valve opening degree at the valve fully-closing state is inputted from the main controller, the driving signal corresponding to a valve fully-closing state is outputted from the valve controller to the coil of the proportional solenoid valve, and if a 20 mA current signal is inputted, the driving signal corresponding to a valve fully-opening state is outputted from the valve controller to the proportional solenoid valve. Similarly, when a 0 V voltage signal as a command signal for setting the valve opening degree at the valve fully-closing state is inputted, the driving signal corresponding to a valve fully-closing state is outputted to the coil, and when a 10 V voltage signal is inputted, the driving signal corresponding to the valve fully-opening state is outputted to the coil.